1. Field of the Invention
In general, the present invention relates to hydrogen diffusion cells. More particularly, the present invention relates to hydrogen diffusion cells that contain wound coils of palladium tubing.
2. Description of the Prior Art
In industry, there are many known techniques for separating hydrogen from more complex molecules in order to produce a supply of hydrogen gas. One such technique is electrolysis, wherein hydrogen gas is obtained from water. Regardless of how hydrogen gas is obtained, the collected hydrogen gas is typically contaminated with secondary gases, such as water vapor, hydrocarbons and the like. The types of contaminants in the collected hydrogen gas are dependent upon the technique used to generate the hydrogen gas.
Although contaminated hydrogen gas is useful for certain applications, many other applications require the use of pure hydrogen. As such, the contaminated hydrogen gas must be purified. One technique used to purify hydrogen is to pass the hydrogen through a hydrogen diffusion cell. A typical hydrogen diffusion cell contains at least one coil of palladium tubing. The palladium tubing is heated and the contaminated hydrogen gas is directed through the palladium tubing. When heated, the palladium tubing is permeable to hydrogen gas but not to the contaminants that may be mixed with the hydrogen gas. As such, nearly pure hydrogen passes through the palladium tubing and is collected for use.
To make the hydrogen gas permeate through the palladium tubing, a pressure differential is typically maintained between the pressure of the contaminated hydrogen gas within the palladium tubing and the pressure of the purified hydrogen gas surrounding the palladium tubing. During the operation of the hydrogen diffusion cell, this pressure differential is typically kept at about twenty pounds per square inch. The structure of the palladium tubing is adequate to operate within this pressure differential without rupturing or otherwise deforming, provided that the pressure within the tubing is greater than the pressure surrounding the tubing. However, on occasions, improper operation and maintenance practices may produce a reverse pressure differential within the hydrogen diffusion cell. During a period of a reverse pressure differential, the pressure surrounding the palladium tubing surpasses the pressure within the palladium tubing. Since, the palladium tubing is typically very thin, only a small reverse pressure differential can cause the palladium tube to collapse.
Periods of reverse pressure differential typically occur during maintenance periods or when the hydrogen diffusion cell is first shut down. When the hydrogen diffusion cell is running properly, the pressure of the contaminated hydrogen gas within the palladium tubing and the pressure of the gas surrounding the palladium tubing are well controlled. However, when the hydrogen diffusion cell is shut off, an operator often vents the contaminated hydrogen gas from within the palladium tubing before venting the pressure of the purified hydrogen gas surrounding the palladium tubing. This results in a reverse pressure differential that can damage the palladium tubing.
A need therefore exists for a system and method of preventing a hydrogen diffusion cell from experiencing reverse pressure to a degree that can cause damage to the palladium tubing within the hydrogen diffusion cell. This need is met by the present invention as it is described and claimed below.